1. Field of the Invention
The present invention relates generally to the field of molecular biology, and more specifically, to a method for controlling the yeast-to-filamentous growth transition in fungi.
2. Description of the Related Art
The present invention addresses the need to treat and/or control human fungal infections, such as those caused by Candida albicans (C. albicans). C. albicans causes both superficial and disseminated (systemic) infections in humans, and is the leading cause of fungal disease in humans [1]. C. albicans is an opportunistic pathogen of immunocompromised hosts, including AIDS patients, individuals undergoing cancer chemotherapy, individuals receiving immunosuppressive drugs in preparation for tissue transplants, individuals receiving antibiotic treatments and individuals with central venous catheters. Studies indicate that up to 90% of AIDS patients suffer from oropharyngeal and esophageal candidiasis, in which C. albicans is the major causative agent [2]. It is estimated that C. albicans infections result in approximately 5,000 deaths per year in the United States [3]. The high incidence of fungal disease in the immunocompromised patient population indicates a need for better anti-fungal treatment modalities and anti-fungal drugs.
C. albicans is able to grow in different morphological forms, such as budding yeast (round or oval cells) and a range of filamentous forms that include true hyphae and pseudohyphae [4]. An essential component of the virulence of C. albicans is its ability to change between the yeast growth form and the filamentous growth forms. As used herein, the term “filamentous growth forms” includes both hyphal growth forms and pseudohyphal growth forms. Mutations that block transitions between these growth forms, and therefore restrict the organism to one of these two growth forms, also significantly reduce the virulence of the organism in mouse models of disseminated candidiasis [5, 11]. Thus, one way of controlling fungal infections in humans may be to prevent or inhibit the yeast-to-filamentous growth transition through small bioactive molecules.
The present invention is based on the unexpected discovery that the small molecule 5-(p-Bromobenzylidine)-α-isopropyl-4-oxo-2-thioxo-3-thiozolidineacetic acid (hereafter referred to as BH3I-1), a previously identified inducer of programmed cell death (PGD) in mammalian cells, inhibits the yeast-to-filamentous growth transition in C. albicans. In mammalian cells, POD is regulated by the Bcl-2 family proteins Bcl-2, Bcl-1x, Bak and Bax. The Bak/Bax proteins induce PGD by permeabilizing the outer mitochondrial membrane, causing the release of death-promoting factors such as cytochrome C and activation of the caspase cascade. Bcl-2 and Bcl-1x are anti-PGD proteins in that they directly antagonize Bak/Bax through protein-protein interactions. The small molecule BH3I-1 induces PGD by specifically binding to Bcl-1x, thereby preventing the antagonistic interaction between Bcl-1x and the Bak/Bax proteins. Surprisingly, especially in light of our discovery of the novel anti-fungal properties of BH3I-1, bioinformatics approaches have indicated that fungal genomes do not encode recognizable Bcl-2 family proteins or proteins with Bcl-2-homology-3 domains [6, 7]. This suggests that BH3I-1 is acting on a target in C. albicans that does not contain a BH3 domain and that is unrelated to the known target of BH3I-1 in mammalian cells.